I spawned skeletons onto waterlogged top slabs, and the second they moved they started going really fast (as if they had speed 3), so then i spawned creepers to try to kill the skeletons (I'm not good at commands) but when they exploded they didn't break any blocks

To recreate this behavior,

First, build top slabs

Then, right click every slab with water (or you can build the slabs in a lake and/or ocean

Next, spawn skeletons  and creepers

Finally, watch as the skeletons go waaay faster than they are supposed to and ignite the creepers (with a flint and steel) and see as they explode and break NOTHNG.